In preparation of thin film through thin film deposition, in particular in chemical vapor deposition and atomic layer deposition, highly pure precursors that can be easily deposited at low temperatures are required for ideal thin film deposition needed in semiconductor processes and various other fields. Especially, germanium precursors are used in silicon-germanium solar cells, optical coatings, or the like. Recently, they are used in various fields including the manufacture of GeSbTe (GST) thin film as next-generation semiconductor device.
In general, germane (GeH4) is used as a germanium precursor in producing germanium thin film or germanium-containing compound thin film. Germane is toxic gas in standard condition and is difficult to handle. Therefore, it needs safety equipment for process application. In addition, it is restricted in use in semiconductor processes requiring low temperature, since a deposition temperature of about 500° C. or higher is necessary for chemical vapor deposition (CVD). For other organometallic germanium precursors, those with alkyl (R), alkoxy (OR) or cyclopentadiene (Cp) groups as ligand are reported. However, because large steric hindrance occurring due to the ligands, these precursors are solid at room temperature or tend to be associated with thin film contamination during deposition (Veprek, S., Glatz, F.; Knowitschny, R. J. Non-Cryst. Solids 1991, 137 and 138, 779; Seigi Suh and David M. Hoffman, Inorg. Chem. 1996, 35, 6164-6169; Henry Gerung, Scott D. Bunge, Timothy J. Boyle, C. Jeffrey Brinkerab and Sang M. Han, Chem. Commun., 2005 1914-1916).
US Patent Application No. 2003/0111013 (Oosterlaken, et al.) discloses deposition methods of silicon germanium layer for thin film preparation using mono-, di-, tri- or tetrachlorogermane. However, these compounds are not appropriate for deposition of germanium because they are decomposed at low temperature.
Korean Patent Application No. 2007-0042805 (Chang-kyun Kim, et al.) discloses a method for preparing a germanium(II) complex with an aminoalkoxide ligand. This compound is a liquid material which is decomposed approximately at 236° C.
Recently, there have been patents and researches about the preparation of GST thin film and related precursor for the manufacture of phase-change random access memory (PRAM). PCT/US2007/063830 (Hunks, et al.) discloses deposition methods of GST thin film using a germanium precursor with an alkylamino ligand, and Korean Patent Application No. 2004/0112906 (Beom-seok Seo, at al.) discloses deposition methods of GST thin film using a germanium(IV) precursor with a silylamino ligand.